Process for producing secondary alkyl primary amines from n-paraffin

ABSTRACT

A process for converting mixtures of C 6  to C 30  n-paraffin and n-paraffin by-products to substantially pure n-paraffin which comprises catalytically hydrogenating the mixture at a temperature of from about 600° to 750° F. in the presence of a Group VIII metal on alumina catalyst where the catalyst contains from about 0.05 to 2.0 weight percent of an alkali metal oxide or alkaline earth metal oxide or thallous oxide. The catalyst can additionally contain a Group VIB or VIIB metal.

This is a division of application Ser. No. 428,638, filed Dec. 26, 1973.

This invention relates to a process for converting mixtures containingn-paraffins to substantially pure n-paraffins. In particular thisinvention relates to a process for converting mixtures of C₆ to C₃₀n-paraffins and C₆ to C₃₀ by-products to substantially pure C₆ to C₃₀n-paraffins by catalytic hydrogenation.

Normal paraffin hydrocarbons having from 6 to 30 carbon atoms representvaluable feedstock materials which can be converted to highly desirableproducts including amines by nitration and hydrogenation or to oximes byphotonitrosation or to secondary alcohols by oxidation. In theillustrative processes described above, from about 5 to 50 weightpercent of the normal paraffin undergoes conversion which results in theformation of a crude product mixture containing not only the desiredmaterial and unconverted paraffin but additionally substantial amountsof oxygenated paraffin by-products which can in some instances beproduced in equal quantities with the sought after product. The desiredproduct, for example, the amine or oxime or secondary alcohol isseparated and recovered from the crude reaction product leaving araffinate composed of a mixture of n-paraffin and oxygenated n-paraffin.While the raffinate may be recycled for further conversion to thepreselected product, the presence of the oxygenated compounds presentinnumerable problems including the substantial buildup of undesiredby-products and the further conversion of the oxygenated hydrocarbons tomultifunctional materials. The formation and buildup of substantialamounts of by-products in turn seriously reduces the attractiveness andselectivity of the process which ultimately leads to a highlyunsatisfactory and cost prohibitive operation.

Heretofore, the n-paraffins contained in the mixture have been purifiedemploying various procedures including the use of molecular sieveselective adsorbents to provide streams suitable for recyclesubstantially free of contaminants. However, this procedure isobjectionable in that it removes substantial amounts of paraffinby-products, which by-products must be ultimately disposed of. Thisoperation is particularly costly where by-product formation approximatesthe amount of desired product originally formed. Other techniquesinvolved upgrading the mixture by hydrogenating crude normal paraffinmixtures containing oxygenated paraffins at temperatures of from about450° to 600° F. in the presence of previously disclosed hydrogenationcatalysts. However, even at this temperature range some hydrocracking tolight paraffins and hydrogenolysis to methane occurred leading to lossesin recoverable recycle material. Further, temperatures in excess of 600°F. were to be avoided as the same caused excessive undesirableisomerization, hydrocracking, hydrogenolysis and coking of thehydrocarbons to, for example, isoparaffins and methane. Whilehydrogenation of the crude mixture at 450° to 600° F. is notparticularly effective inasmuch as some hydrocracking and isomerizationoccurs which reduces the amount of valuable feedstock which can berecycled, the oxygenated by-products are only partially hydrogenatedsuch that a considerable amount of incompletely converted by-productsare recycled.

It is therefore an object of this invention to provide a process whichprovides substantially pure n-paraffins from mixtures of n-paraffin andoxygenated paraffin hydrocarbons in high yields.

Another object of this invention is to provide a process for convertinga mixture of n-paraffin and oxygenated paraffin to substantially puren-paraffin.

Yet another object of this invention is to provide a process whereinmixtures of n-paraffins and oxygenated paraffin hydrocarbons arecontinuously converted to pure n-paraffin compositions.

Other objects and advantages will become apparent from a reading of thefollowing detailed description and examples.

SUMMARY OF THE INVENTION

Broadly this invention contemplates a process for converting a mixtureof n-paraffin and n-paraffin by-products, that is, oxygenated paraffin,to substantially pure n-paraffin which comprises catalyticallyhydrogenating the mixture at a temperature of from about 600° to 750°F., preferably from 610° to 700° F., in the presence of a catalystcomposed of alumina, a Group VIII metal and from about 0.05 to 2.0weight percent of an alkali metal oxide, alkaline earth metal oxide orthallous oxide. The catalyst can also contain as a component thereof anoxide of a member from Group VIB or a member from Group VIIB.

The catalyst employed in our process is one which comprises a member ofGroup VIII of the Periodic Table, alumina and an alkali metal oxide oralkaline earth metal oxide or thallous oxide. Exemplary of the GroupVIII metals are platinum, palladium, rhodium and ruthenium. Nickel andcobalt are also contemplated preferably in combination with a Group VIBmetal oxide such as molybdenum oxide or tungsten oxide. A Group VIIBmember such as rhenium present as the metal can also be used incombination with the Group VIII metal. Aluminas in various forms may beused as a component of the catalyst and particularly those aluminashaving replaceable surface hydroxyl groups and surface areas of from 50to 400 square meters per gram using the BET method. Included within ourdefinition of alumina we mention, for example, eta-alumina,gamma-alumina, silica stabilized aluminas, i.e. aluminas containing upto approximately 5 weight percent SiO₂, thoria-alumina,zirconia-alumina, titania-alumina and chromia-alumina. The Group VIIImetal is present in amounts ranging from about 0.1 to 5.0 weightpercent, preferably from about 0.1 to 2.0 weight percent, for the noblemetals and from 1 to 5 percent for nickel and/or cobalt, based on thecomposite catalyst. The Group VIB metal oxide component when presentranges from about 5 to 20 weight percent of the composite catalyst. TheGroup VIIB metal can be present in an amount of from about 0.1 to 2.0weight percent.

The catalyst described above to be selective in converting the mixtureof n-paraffin and oxygenated paraffin to substantially pure n-paraffinat a temperature of from about 600° to 750° F. requires as a componentthereof from about 0.05 to 2.0 weight percent of an alkali metal oxide,alkaline earth metal oxide or thallous oxide or mixtures thereof.Illustrative of the alkali metals contemplated we mention lithium,sodium, potassium, rubidium and cesium and as the alkaline earth metalscalcium, strontium and barium. The presence of the additional componentmoderates the activity of the Group VIII metal on alumina catalyst whichin the absence thereof and at hydrogenation temperatures of from about600° to 750° F. otherwise causes substantial isomerization andhydrocracking of the mixture to isoparaffins and light paraffins. Thepresence of the minor amount of alkali metal oxide, alkaline earth metaloxide or thallous oxide and mixtures or combinations thereof on thecatalyst deters isomerization and hydrocracking of the mixture includingthe n-paraffin and by-products and thereby selectively converts theby-products to valuable n-paraffin recycle feedstock.

The catalyst described above can be prepared by introducing the GroupVIII metal, and when desired the Group VIB or VIIB member, to thealumina by impregnating with an aqueous solution of a soluble salt ofthe metal followed by drying and calcination at a temperature of from600° to 1200° F. for several hours. The alkali metal oxide, alkalineearth metal oxide or thallous oxide can likewise be introduced to thealumina by impregnating with a soluble salt, such as the nitrate oracetate, either simultaneously with or subsequent to the introduction ofthe Group VIII metal followed by drying and calcination at 600° to 1200°F.

The alumina component of the catalyst complements the hydrogenatingactivity of the Group VIII metal and moderator by promoting thedehydration of alcohols or glycols present to the corresponding olefinwhich are in turn hydrogenated to n-paraffin. This property of thecatalyst is particularly beneficial not only at the operativehydrogenation temperature range of from 600° to 750° F., but the dualfunctional aspect of the catalyst is particularly advantageous inconverting any olefinic material formed at the elevated temperatures andpartially converted to n-paraffin to be essentially converted ton-paraffin by an additional and subsequent hydrogenation undertaken atabout 450° to 650° F.

In a further embodiment, the mixture of C₆ to C₃₀ n-paraffin andoxygenated paraffin is initially hydrogenated at a temperature of fromabout 350° to 500° F., preferably from about 400° to 450° F., and priorto the hydrogenation at 600° to 750° F. described above. Initialhydrogenation is particularly desirable when the mixture contains suchoxygenated components as, for example, nitrites or nitrates which arethermally unstable at temperatures of 600° F. and higher. Suchillustrative thermally unstable materials when introduced to reactorpreheaters operated to raise the temperature of the mixture to about600° to 750° F. prior to introduction of the mixture into thehydrogenation reaction, thermally decompose and form resinous depositsin the preheater. By initially hydrogenating the mixture at 350° to 500°F., the thermally unstable materials are converted to more stable formswhich can thereafter be successfully heated to temperatures of 600° F.and higher in reactor preheaters. The initial hydrogenation also servesas a guard chamber to protect the catalyst employed at the 600° to 750°F. hydrogenation to convert some oxygenates to non-volatile inorganiccompounds such as when the mixture contains alkyl borate estersdescribed below. Conventional hydrogenation catalysts can be employed inthe initial hydrogenation as, for example, nickel, cobalt, platinum,palladium and rhodium. The catalysts can be supported on kieslguhr,silica, carbon or alumina as is known in the art. The catalyst describedabove and employed at the hydrogenation conditions of 600° to 750° F.can also be used.

In some instances it may be desirable to pass the recycle mixturethrough a bed of alumina, silica gel or activated carbon to act as guardcase for the hydrogenation catalyst. Illustratively, a recycle mixturederived from the conversion of paraffins to secondary alcohols willcontain minor amounts of boric acid and borate esters which adverselyeffect hydrogenation catalysts. Such materials can be effectivelyremoved from the mixture prior to hydrogenation by, for example, passingthe mixture at 400° to 500° F. through a bed of activated alumina.

As mentioned above, an additional and subsequent hydrogenation may alsobe desirable as, for example, when the liquid product hydrogenated at600° to 750° F. is found to contain minor amounts of C₆ to C₃₀ olefins.Such an additional hydrogenation treatment can be conducted at fromabout 450° to 650° F. wherein the olefin is converted to n-paraffinemploying catalysts of the type described in connection with thehydrogenation at 600° to 750° F.

In general, hydrogenation in each of the above plural temperature rangesis undertaken in the presence of hydrogen at pressures ranging fromabout 100 to 1500 p.s.i.g. for periods of from 0.2 to 5 hours. Incontinuous processing the mixture can be introduced into thehydrogenation zones at space velocities of from 0.2 to 10.0 volumes ofliquid feed per volume of catalyst per hour (v./v./hr.)

The mixtures hydrogenated according to the instant invention andcomposed of n-paraffins having from 6 to 30 carbon atoms and n-paraffinby-products, that is, oxygenated paraffins having from 6 to 30 carbonatoms can be derived from a plurality of sources. Typically, the mixturecontemplated for hydrogenation in accordance with the instant inventionis predominantly C₆ to C₃₀ n-paraffin containing from 0.5 to 30 weightpercent oxygenated paraffins. Representative of the C₆ to C₃₀ oxygenatedparaffins are alcohols, ketones and polyoxygenated materials such asacids, esters, glycols, lactams, ketoacids, and ketoalcohols. Themixture depending upon its source can also contain additional materialscapable of being converted to normal paraffins in the presence of thecatalyst described above and under the hydrogenation conditions recited.Among such materials are included C₆ to C₃₀ nitroparaffins, secondaryamines, diamines, nitroalcohols, aminoalcohols, aminoketones,nitroketones, nitrates, nitrites, dinitroparaffins, alkylchlorides andolefins.

Illustrative of the sources of the mixtures hydrogenated herein wemention the following. In the production of secondary alkyl primaryamines from n-paraffins having from 6 to 30 carbon atoms, the amines areprepared by nitrating from about 5 to 50 weight percent of the paraffinto nitroparaffin employing as nitrating agent, for example, nitric acid,nitrogen dioxide or dinitrogen tetroxide at a temperature of from about250° to 500° F. to form a crude nitrated product containing in additionto unconverted n-paraffin and nitroparaffin substantial quantities ofoxygenated by-products such as C₆ to C₃₀ ketones, alcohols, carboxylicacids, nitrites, nitrates and multifunctional materials such asdinitroparaffins, nitroalcohols, nitroketones and ketoalcohols.Thereafter the crude nitrated liquid product typically comprising from50 to 94.5 weight percent unreacted n-paraffin, 5 to 35 weight percentnitroparaffin and 0.5 to 15 weight percent oxygenated by-products isintroduced to a hydrogenation zone where the nitroparaffin ishydrogenated to the amine at average conversion temperatures rangingfrom about 100° to 450° F. in the presence of conventional and wellknown hydrogenation catalysts. A preferred catalyst is palladium oncarbon. The crude liquid hydrogenated product comprises C₆ to C₃₀n-paraffin secondary alkyl primary amine and oxygenated by-products suchas acids, alcohols, ketones, ketoalcohols, aminoalcohols, aminoketones,nitrates and nitrites. Other by-products such as unreactednitroparaffin, secondary amines and diamines can also be present. Theprimary amine is separated form the liquid hydrogenated productemploying conventional recovery procedures such as step-wisefractionation or the amine may be converted and recovered as an aminesalt by reaction of the crude liquid product with an inorganic acidfollowed by further treatment of the amine salt with alkali andthereafter recovering the primary amine by distillation. The unreactednitroparaffin and oxygenated or other by-products of the nitrationhydrogenation reactions in admixture with the paraffin, secondary aminesand diamines separated from the primary amine represent a typicalmixture contemplated by the instant invention which is hydrogenated tosubstantially pure n-paraffin.

The production of secondary alcohols from C₆ to C₃₀ n-paraffins alsoprovides by-product streams composed of mixtures of n-paraffin andoxygenated paraffins which are according to the instant inventionconverted to substantially pure n-paraffin. The production of secondaryalcohols from C₆ to C₃₀ paraffins is accomplished by contacting theparaffin in the liquid phase with an oxygen containing gas in thepresence of boric acid at a temperature of from about 300° to 450° F. toconvert from 5 to 50 weight percent of the paraffin to a mixture ofalkyl borate esters, unreacted paraffin and degradation productsincluding olefins and oxygenated products other than the borate esters.The mixture is first fractionated to separate an overhead fractioncomprising unreacted n-paraffins, a portion of the by-products includingsuch materials as olefins, ketones, some alcohols and traces of borateester, and a bottoms fraction containing the borate ester andpolyoxygenated by-products including ketoalcohols, acids, ketoacids andglycols. The bottoms are contacted with water at from 100° to 212° F. tohydrolyze the borate esters to secondary alcohols which bottoms separateinto two phases comprising a top organic layer containing secondaryalcohol and substantially all of the polyoxygenated products and abottom layer comprised of aqueous boric acid, which layers areseparated. The organic layer is fractionated to separate desiredsecondary alcohols as an overhead and a bottoms comprisingpolyoxygenated materials. The overhead recovered by the firstfractionation comprised of unreacted n-paraffins, olefin and oxygenatedproducts including alcohols and ketones represents a typical mixturecontemplated for hydrogenation according to the instant invention. Allor a portion of the final organic bottoms containing the polyoxygenatedby-products can also be included into the mixture contemplated forhydrogenation herein.

Another process providing mixtures of n-paraffin and oxygenatedparaffins, which according to the instant invention can be substantiallyconverted to pure n-paraffins, involves the production of normalparaffin oximes having from 6 to 30 carbon atoms from normal paraffins.The oximes are prepared by photochemically reacting and converting from5 to 50 weight percent of a C₆ to C₃₀ normal paraffin with a gaseousnitrosating agent, such as nitrosyl halides, nitrosyl sulfuric acid,nitrogen oxide and chlorine or nitrogen peroxide and chlorine at atemperature of from about 30° to 140° F. under the influence of light toproduce normal paraffin oximes and up to about 5 weight percentoxygenated by-products primarily composed of ketones. Somealkylchlorides are also formed. The oxime is thereafter converted to thesulfate and unconverted C₆ to C₃₀ paraffin, ketones and alkylchloridesare extracted using a low boiling hydrocarbon such as cyclohexane,n-pentane, isoheptane or petroleum ether. Thereafter the low boilinghydrocarbon is separated by distillation and the mixture of then-paraffin, oxygenated paraffin, in this instance ketones, along withthe alkylchlorides, can be converted to substantially pure n-paraffinaccording to the instant invention.

It will be appreciated that other known processes providing mixtures ofn-paraffin and oxygenated paraffin by-products can be improved byapplicants' catalytic hydrogenation and that the processes mentionedabove are merely illustrative and are not intended to limit theinstantly claimed invention.

In order to illustrate more fully the nature of our invention and mannerof practicing the same, the following examples are presented. In theseexamples the best mode contemplated by us for carrying out our inventionis set forth.

EXAMPLE I

The conversion of n-paraffins to secondary alkyl primary amines isundertaken by providing a fresh water-white C₁₀ to C₁₄ n-paraffinhydrocarbon composition having the following carbon chain lengthdistribution on a weight percent basis: C₁₀ 11.1, C₁₁ 28.7, C₁₂ 32.2,C₁₃ 26.9, C₁₄ 1.1. To 10.7 weight percent of fresh normal paraffinsthere is mixed 89.3 weight percent of previously processed and upgradedrecycle paraffins according to the instant invention.

A paraffin hydrocarbon charge at the rate of 940 pounds per hour isnitrated with 60 pounds per hour of nitrogen dioxide wherein nitrationproceeds at 330° F. under a pressure of 4 p.s.i.g. Off-gases comprisingparaffin, nitrogen dioxide, nitric oxide, nitrous oxide, nitrogen,carbon dioxide, carbon monoxide and water are withdrawn, the off-gasespartially condensed, and condensed paraffin recycled. Nitric oxide inthe overhead gas is oxidized to nitrogen dioxide, the oxidized gascooled to condense nitrogen dioxide, and the liquefied nitrating agentrecycled. Non-condensible gases including nitrogen, nitric oxide,nitrous oxide, carbon monoxide and carbon dioxide are vented.

The crude nitrated paraffin product, 977 pounds, comprising 80 weightpercent n-paraffin, 14.7 weight percent nitroparaffin and 4.4 weightpercent by-products including oxidized paraffin and polyfunctionals ofwhich 0.6 weight percent are ketones, 1.2 weight percent are nitritesand 0.5 weight percent are nitrates is continuously caustic washed withabout 70 pounds per hour of 10 percent aqueous sodium hydroxide in aline mixer at 200° F. and 50 p.s.i.g. The resulting aqueous layer isseparated in a settler and removed. The organic layer is washed at 180°F. and 50 p.s.i.g. with 27 pounds per hour of water in a conventionalcountercurrent extraction tower. The washed nitrate product contains 129pounds of nitrated paraffin and 833 pounds of n-paraffin and othermaterials that include 0.43 weight percent ketones, 0.95 weight percentnitrites and 0.41 weight percent nitrates.

The crude nitrated paraffin composition is introduced at an inlettemperature of 200° F. to a hydrogenation reactor containing ahydrogenation catalyst composed of one weight percent palladium oncarbon at a liquid hourly space velocity of 2.0 volumes of liquid pervolume of catalyst per hour. Hydrogenation is conducted under a hydrogenpressure of 560 p.s.i.g. and up to a maximum conversion temperature of410° F. Following hydrogenation, substantially all of the nitroparaffinis reduced to amine. Hydrogen, ammonia and some water are removed asgases and remaining water and ammonia are decanted from the recoveredcrude hydrogenation product at 110° F.

The crude hydrogenation product at a rate of 950 pounds per hourcomprising 834 pounds of n-paraffins and miscellaneous by-productsincluding 0.49 weight percent amines (secondary) and 0.52 weight percentketones, 100 pounds of secondary alkyl primary amines, about 1 pound ofunconverted nitroparaffins and 15 pounds of water and ammonia iscontacted and saturated with 87 pounds per hour of carbon dioxide at 300p.s.i.g. and 110° F. thereby forming an amine-carbon dioxide complex.The carbon dioxide saturated crude hydrogenation product iscounter-currently contacted in a tower with 1,500 pounds per hour of asolvent mixture comprising 40 percent methanol and 60 percent water, thesolvent mixture having been previously saturated with 50 pounds per hourof carbon dioxide at 300 p.s.i.g. and 110° F. Upon contacting of thecarbon dioxide saturated crude hydrogenation product with the solventmixture, the primary amine complex transfers from the predominantlyparaffin stream to the solvent stream.

The amine depleted paraffin stream is subsequently reduced toatmospheric pressure in a flash drum whereupon carbon dioxide therein isremoved overhead. The amine-enriched solvent stream is heated to atemperature of 150° F, and introduced to a flash tower maintained atatmospheric pressure where carbon dioxide, along with some methanol andwater, is removed overhead. The amine-rich liquid from the flash toweris passed through a fractionator where methanol, residual carbon dioxideand some water are removed overhead. The bottom stream containing waterand crude amines separates as two phases, namely a water phasecontaining some methanol and amines, and a crude amine phase containingsome water.

110 pounds per hour of the crude amine phase are heated to 248° F. andflashed at 160 mm. Hg thereby removing as overhead substantially all ofthe residual methanol and water, along with some organic materials.After condensation, the organic matter in the overhead is separated fromthe aqueous layer and combined with the flashed amine phase. The flashedcrude amine phase is thereafter vacuum-distilled at 20 mm. Hg and 200°F. to remove overhead residual methanol, water, paraffinic hydrocarbonsand lighter than C₁₀ amines. Finally, the amine phase is vacuumdistilled at 10 mm. Hg and 300° F. to produce 100 pounds per hour offinished amine containing 98.5 weight percent secondary alkyl primaryamine.

The amber colored amine-depleted paraffin stream from the raffinateflash drum is combined with the predominantly paraffinic waste streamsderived from vacuum distilling the crude amines to form a recycle streamcomprising about 98 weight percent n-paraffin, 0.15 weight percentnitroparaffins and about 1.85 weight percent by-products. The mixedrecycle stream is introduced into an initial hydrogenation zone at therate of 840 pounds per hour and hydrogenated at 400° F. with 17 poundsper hour of hydrogen at 500 p.s.i.g. at a liquid hourly space velocityof 3.0 in the presence of a nickel-molybdenum on alumina catalyst. Theproduct of the initial hydrogenation zone is introduced into asubsequent hydrogenation zone at the rate of 840 pounds per hour andhydrogenated at 660° F. with 16 pounds per hour of hydrogen at 500p.s.i.g. at a liquid hourly space velocity of 1.5 in the presence of a 3weight percent nickel oxide--12 weight percent molybdenum oxide-- 0.6weight percent barium oxide on alumina catalyst. After separatinghydrogen, ammonia and water, the hydrogenated water-white product isessentially free of nitrated and oxygenated by-products and is recycledfor introduction to the nitration reactor. The system for producing theamines continues to operate for long periods of time withoutinterruption.

EXAMPLE II

An amine-depleted C₁₀ to C₁₄ paraffin stream composed of about 3 weightpercent by-products including nitroparaffins, ketones, secondary amines,alcohols, nitrates, nitrites and polyfunctional derivatives of then-paraffin similar to Example I was introduced into a hydrogenationreactor containing a nickel on kieselguhr hydrogenation catalyst at therate of 3.3 pounds per hour and hydrogenated at 610° to 615° F. with0.03 pounds per hour of hydrogen at about 600 p.s.i.g. Sampling of theoff-gas shows it to contain 7 percent methane thereby demonstrating thatsubstantial hydrocracking has occurred.

EXAMPLE III

A continuous process for converting n-paraffin to secondary alcohols isundertaken by introducing a C₁₀ to C₁₄ n-paraffin charge composed of12.6 weight percent fresh n-paraffifn and 87.4 weight percent recyclen-paraffin hydrogenated according to this invention.

815 pounds per hour of the paraffin charge is preheated to 350° F. andintroduced to two continuous stirred tank reactors in series along withorthoboric acid, the acid added at the rate of 2.1 weight percent basistotal paraffin charge to each reactor for a total of 4.2 weight percentboric acid basis the total paraffin charge. Air is introduced to eachreactor in the amount of 1.3 SCF per hour per pound of paraffin presentin the first reactor and at the rate of 0.7 SCF/hr./lb. in the secondreactor. The reactors are operated at 10 p.s.i.g. and are each equippedwith means to separate overhead by-product water. The average residencetime of the paraffin in the first reactor is 3.1 hours and in the secondreactor 2.6 hours, thereby providing a total conversion of paraffin to17.1 weight percent borate esters, about 0.55 weight percent oxygenates,and about 0.1 weight percent olefins, with the remainder of the organicmaterial being unconverted paraffin. The reactor effluent stream isfirst fractionated by vacuum stipping at 365° F. and 5 mm pressure toobtain a bottom stream of stripped borate esters and an overheadcontaining predominantly C₁₀ to C₁₄ unreacted n-paraffin, 0.2 weightpercent secondary alcohols, 0.1 weight percent olefins, 0.12 weightpercent acids, 0.24 weight percent ketones and 0.54 weight percentborate esters. The bottom stream of stripped borate esters, otherpolyoxygenated by-products and traces of unreacted n-paraffin arecontacted with water at 180° F. in an in-line mixer at a weight ratio ofwater to borate ester containing stream of 2:1 and a top organic layeris separated from a bottom layer composed of aqueous boric acid.

The top organic layer composed of 85 weight percent secondary alcohols,0.6 weight percent unreacted paraffins, 1.2 weight percent boric acidand the remainder polyoxygenated paraffins is fractionated at 390° F.and 2 mm pressure to remove overhead 101 pounds of secondary alcohols ofapproximately 99 percent purity. The bottoms comprising C₁₀ to C₁₄polyoxygenated paraffins are steam stripped to form an overhead composedof 30 weight percent acids, 12 weight percent ketones, 38 weight percentglycols, 17 weight percent esters and 3 weight percent boric acid. Thisoverhead is combined with the first fractionated overhead containingpredominantly C₁₀ to C₁₄ unreacted paraffin to form a recycle streamcomprising 0.1 weight percent olefin, 0.5 weight percent acids, 0.4weight percent ketones, 0.5 weight percent glycols, 0.7 weight percentborate esters, 0.4 weight percent boric acid and the remainder unreactedparaffin.

The recycle stream is introduced into an initial hydrogenation reactorat the rate of about 722 pounds per hour and hydrogenated at 400° F.with 25 pounds per hour of hydrogen at 800 p.s.i.g. at a liquid hourlyspace velocity of 2.5 in the presence of a cobalt-molybdenum on aluminacatalyst. The product of the initial hydrogenation zone is introducedinto a subsequent hydrogenation reactor at the rate of 719 pounds perhour and hydrogenated at 670° F. with 25 pounds per hour of hydrogen at800 p.s.i.g. at a liquid hourly space velocity of 2.0 in the presence ofa 0.75 weight percent platinum, 0.4 weight percent potassium oxide ongamma alumina catalyst. After separating hydrogen and water, thehydrogenated product is essentially free of oxygenated by-products, then-paraffin content is in excess of 99 weight percent and the product isrecycled for introduction to the stirred tank reactors. Virtually nomethane, light hydrocarbons and isoparaffins are produced duringhydrogenation. For 101 pounds of 99 percent purity secondary alcohol,there is required 103 pounds of fresh n-paraffin feed in the continuousprocess.

EXAMPLE IV

A recycle stream similar to that in Example III is hydrogenated at 550°F. and 800 p.s.i.g. with 3.5 pounds of hydrogen per 100 pounds ofrecycle feed over a nickel on kieselguhr hydrogenation catalyst at aliquid hourly space velocity of 2.0. About 12 weight percent of the feedis converted to paraffins lighter than C₆. For 101 pounds of 99 percentpurity secondary alcohol, there is required 115 pounds of freshn-paraffin feed in the continuous process employing the catalytichydrogenation described in this example. It will be seen that theclaimed invention employing the catalyst illustrated in Example III ismore selective in converting the mixture to n-paraffin than theconventional hydrogenation catalyst employed in Example IV.

EXAMPLE V

Example III is repeated except that the recycle stream is firstintroduced through a bed of alumina at 400° F. acting as a guard chamberand thereafter catalytic hydrogenation of the recycle stream isundertaken at 670° F. in the presence of a 3.0 weight percent nickeloxide -- 12.0 weight percent molybdenum oxide -- 0.2 weight percentlithium oxide on eta alumina catalyst. The results of hydrogenation andthe composition of the hydrogenated product are similar to Example III.

We claim:
 1. In a process for producing secondary alkyl primary aminesfrom n-paraffin reactant wherein a portion of said n-paraffin isnitrated to form a nitroparaffin along with nitrated and oxygenatedby-products, wherein said nitroparaffin is substantially hydrogenated tosaid amine and where said amine is separated from a mixture of unreactedparaffin and oxygenated by-products, the improvement which comprises:(a)catalytically hydrogenating said mixture of unreacted paraffin andoxygenated by-products at a temperature of from about 600° to 750° F. inthe presence of a catalyst composed of alumina, from about 0.1 to 5.0weight percent of a Group VIII metal and from about 0.05 to 2.0 weightpercent of an alkali metal oxide, alkaline earth metal oxide or thallousoxide to substantially pure n-paraffins; and (b) recycling saidn-paraffin product of (a) for nitration with said n-paraffin reactant.2. A process according to claim 1 wherein said mixture is hydrogenatedat from about 610° to 700° F.
 3. A process according to claim 1 whereinsaid mixture is initially hydrogenated at from about 350° to 500° F. 4.A process according to claim 1 wherein said mixture is initiallyhydrogenated at from about 400° to 450° F.
 5. A process according toclaim 1 wherein said mixture is additionally hydrogenated at 450° to650° F. prior to recycling in (b).
 6. A process according to claim 1wherein said Group VIII metal is selected from the group consisting ofplatinum, palladium, rhodium, ruthenium, nickel and cobalt.
 7. A processaccording to claim 1 wherein said alkali metal oxide is lithium oxide,sodium oxide, potassium oxide, rubidium oxide or cesium oxide.
 8. Aprocess according to claim 1 wherein said alkaline earth metal oxide iscalcium oxide, strontium oxide or barium oxide.
 9. A process accordingto claim 1 wherein said n-paraffin and oxygenated by-product has from 6to 30 carbon atoms.
 10. A process according to claim 1 wherein saidcatalyst comprises nickel oxide, molybdenum oxide, barium oxide andalumina.
 11. A process according to claim 1 wherein said catalystcomprises platinum, potassium oxide and alumina.